Swagger : Swagger is a powerful open source framework backed by a large ecosystem of tools that helps you design, build, document, and consume your RESTful APIs...
API Security Checklist : Checklist of the most important security countermeasures when designing, testing, and releasing your API.
DevDocs : DevDocs combines multiple API documentations in a fast, organized, and searchable interface.
JSON Schema : JSON Schema is a vocabulary that allows you to annotate and validate JSON documents.
This guide describes a set of HTTP+JSON API design practices, originally extracted from work on the Heroku Platform API.